Ink pad



IIIIIflIIA y 1952 w. D. ROBBINS 2,596,725

INK PAD Filed July 5, 1947 INVENTOR. 14 WINNIE DAVID Rosams ATTORNEYPatented May 13, 1952 INK PAD Winnie David Bobbins, Denton, Tex.,assignor to Clarence Bentley and Ray Crawford, doing business asScientific Ofiice Products, Dallas,

Tex., a partnership Application July 5, 1947, Serial No. 759,035

1 Claim, .1

My invention relates to ink pads of the kind commonly used for rubberstamps, although it is not limited to such use, and has otherappropriate uses. It is an object of my invention to provide an ink padwhich is economical and serviceable, and which delivers a properquantity of ink throughout a long period of useful life.

Another object is the provision of a pad which can be quickly andthoroughly impregnated with ink, either in the process of originalmanufacture, or in renewal after a period of service.

A further object is the provision of an ink pad which will minimizeevaporation of ink from the surface of the pad when it is not in use,and which will in consequence largely eliminate troubles from thickeningof the ink and clogging of rubber stamps experienced with pads in commonuse.

Still another object is the provision of a pad which is adapted tomanufacture by methods which will keep down losses from spoilage and 7rejections arising from distortion of the pad material in themanufacturing process.

With the foregoing and other objects in view, my invention consists inthe improvement in inking pads set forth in the following descriptionand shown in the accompanying drawings, in which:

Figure 1 is a plan View of a pad incorporating my invention;

Figure 2 is an enlarged sectional view of a portion of the pad, taken onthe line 2-2 of Figure 1;

Figure 3 is a plan view of a portion of a pad illustrating a modifiedform of my invention;

Figure 4 is an enlarged sectional view of a portion of the pad of Figure3, taken on the line 4 5; and

Figure 5 is a fragmentary sectional view showing a step in the making ofanother form of pad embodying the principles of my invention.

Perhaps the commonest device for inking the ordinary rubber stamp is theone having a padded portion covered with linen, muslin, or other clothmaterial. The shortcomings of this type are well known-it dries out,rots out, becomes hard, de-- velops a gummy surface, gives up clothparticles to the stamp, or otherwise becomes unsuitable for use,sometimes in a disappointingly short period. Others before mehavetriedto obviate some of these difficulties by using sponge rubber as apad material. -Sponge rubber, however, has its own shortcomings, whichtothe best of my knowledge have not been satisfactorily overcomeheretofore.

I have devised what I believe to be novel means by which sponge rubberor similar material may be employed in an ink pad with entirelysatisfactory results. In the drawings I have used the numeral I0 todesignate a base which has a cavity H formed therein to receive a pad I2of sponge rubber or similar porous, resilient material such as thesynthetic products having rubber-like qualities. The base H! has severalfunctions: it holds the pad in place on the desk, its added weightreducing accidental movement of the assembly when the pad is used; itretains the excess without mess or waste incase the pad is over-inked;but perhaps most important in connection with my invention is that itconfines the pad against lateral expansion when a stamp is pressed onit.

One of the disadvantages of a plain sponge rubber pad is that althoughthe material is porous, it is difficult to impregnate fully with ink. Ido not know the reason for this, but have found by cutting pads openthat they are not well impregnated even after vigorous kneading for someconsiderable time while bathed in ink. Obviously this is a source ofdifficulty both in manufacture of a pad, and in subsequent renewal ofthe ink supply by the user. Furthermore, a new pad would not contain afull supply of ink, and would require renewal sooner than should benecessary.

Allied, doubtless, to the difficulty of inking is the fact that after aperiod of use a sponge rubber pad does not deliver ink readily to theinking surface when a stamp is pressed on it, even though there wouldseem to be enough ink in the interior of the pad. It appears that eventhough the material is porous, it does not permit sufficient freedom forpassage of ink .to and from the/deeper portions of the pad.

The pad as I prefer to make it has a raw cut surface I3 placeduppermost, exposing the porous structure of the sponge. To avoidcomplicating the drawing, I have not endeavored to illustrate thisporous structure in the plan view of Figures 1 and 3. Preferably, thoughnot necessarily, the

bottom of the pad has a solid or non-porous layer or skin surface 14which isnormally present in the material as manufactured. The advantageof this layer is that it helps to retain ink inthe sponge. i

Now to facilitate the inking process I cut perforations or slits iii inthe pad, substantially the full depth of the spongy portion thereof, aswill be seen in the sectional views of Figures 2, 4 and 5. These slitsmake for much freer passage of ink through the pad, facilitate speedyand complete inking, and deliver ink readily to the surface of the padwith a minimum of pressure.

These advantages obtain even in a sponge pad of quite fine grain, whichis desirable for uniformity of inking a stamp.

It will be understood that the slits can be arranged in the pad in avariety of configurations and still contribute the advantages describedwith regard to ink reception, storage and delivcry, but I have found byexperience a number of factors which I consider important, and whichmight not be readily apparent. For one thing, the length of anindividual slit in a given lateral direction must not be too great; aslit which is too long tends to gape when the pressure of a stamp isapplied, and may feed too much ink in certain spots. I have concludedthat conditions are satisfactory when no straight portion of a slit isgreater in a given lateral direction It than the depth ll of the slit inthe pad. The slit 7 may actually continue beyond the dimension thuslimited, but it must undergo a definite change of direction, whichreduces the tendency to gape. And although I define as above the maximumlength of any straight portion of a slit, I consider it preferable thatno slit have a straight portion extending in any given lateral directionfor a distance greater than one-half of the depth of the slit.

A second consideration is that the slits, whether curved or composed ofa series of straight portions, should not be continued to form anenclosed figure, such as a circle or a square. The reason is that thesponge material and the cutting tools are each subject to variation. Theeffort, of course, is to maintain maximum depth of cut, in order to getfull advantage of the slits, yet not cut through the bottom of the pad.If the variables mentioned result in the tool cutting throughoccasionally, the center of an enclosed figure will drop out, and thepad is spoiled.

A third consideration requires somewhat more explanation. An overallpattern of slit figures such as that illustrated in Figure 1 is perhapsbest made by a die having a plurality of punches, one for each star orother figure 18. When the cutting operation is performed, the cuttingedges of the punches contact the surface of the pad and then compress itconsiderably before cutting action begins. During this compression thesponge material in the lower layers tends to fiow out from under eachpunch, until finally the cut reaches these levers. When the pressure isrelieved as the punch is withdrawn, the lower layers contract laterallyagain under each punch. The result is that the figurecut by each punchis substantially smaller at its base than at the sur face [3 of the pad.Thus with an enclosed figure, the center may be so weak at its base thatit will pull out with the punch, or it may break out in use,particularly in coarse grained sponge material. I

The flow of material under each punch as pressure is applied is indirections radial to the center line of the punch, so I prefer to usefigures or groups of slits in which straight slit portions are arrangedradially with respect to a common center line, which can be the same asthe center line of the punch with which the incisions are made. Sincethe slits lie along the directions of flow, the figur will not bedistorted by the cutting operation. Such a figure has the advantages ofuniformity of pattern without the disadvantages of a closed figure.

The slits may be arranged around the center line but not extending toit, as in Figures 3 and 4, or, as in Figures 1 and 2, they may connectat the center. In the latter case I prefer an odd number ofequally-spaced slits; with an odd number, no slits fall in alignment onopposite sides of the center of the figure, so that the change ofdirection previously mentioned is provided for. This is illustrated, forexample, -by the difference in direction-between the direction of thearm l5a in the star figure l8, and either of the most nearly oppositearms |5b or I50.

A modified form of my invention is illustrated in Figure 5, which showsan approximately conical pointed punch pressed into the pad. The cutmade in the pad by such an operation is a vertical line, giving readieraccess of ink to the interior of the pad, though of course not aseffectively as a slit of finite length in a lateral direction. However,it is practical to make a large number of such perforations orpunctures, closely and uniformly spaced over the area of the pad,resulting in substantial improvement in operation over a plain pad. Thistype of perforation is of course a non-enclosed figure, with the ad.-vantages previously pointed out.

With regard to the general spacing of the slits or perforations orgroups thereof in the pad, I consider it preferable to have close enoughspacing so that no point on the surface 13 of the pad is at a distancefrom a perforation greater than the depth ll of the perforations. Thisinsures sufficient uniformity of ink delivery to the surface of the pad.The mechanical requirements of the'perforating operation are such that amarginal area I9 may not fulfill this condition, but this exception isof no great importance when the pad is used.

It will be understood that some changes may be made in the constructionand arrangement of the various parts of an ink pad or in the materialsthereof, without departing from the true spirit and purpose of myinvention,,and it is my intention to cover any and all such modifiedforms as come within the full and proper scope of my claim.

I claim as my invention:

An inking pad comprising a body of spongy, porous, resilient materialhaving groups of slits formed therein, said groups being composed offive slits extending radially from and communicating with a common lineat substantially equiangular spacing, said slits extending downwardlyinto said body more than half the total thickness of said body but notthrough the bottom surface thereof, each slit extending laterally in astraight line for a distance not exceeding the depth of cut.

WINNIE DAVID ROBBINS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,323,487 Payne Dec. 2, 19191,923,114 Partridge Aug. 22, 1933 2,374,198 Harris Apr. 24, 19452,422,814 Alexander June 24, 1947

